This invention relates to flying an unmanned aerial vehicle (UAV) near overhead lines. To fly a UAV safely the US Federal Aviation Administration asks that you address three issues:
sense and avoid other air traffic,
maintain control even with a lost radio link, and
prevent spoofing or jamming of the control signals
This invention addresses the latter two issues for flights near energized overhead lines by including an electromagnetic field sensor on the UAV that automatically shuts down the powertrain when the field strength drops below a preset value. The addition of the sensor and the shutdown mechanism ensure the UAV stays within a certain radial distance of the overhead line, thereby defining a virtual ‘tunnel’ around the overhead lines. Neither a lost radio link, nor malicious spoofing of the communication, nor jamming of the GPS signal, nor autopilot failure, nor incorrect waypoints allow the UAV out of the tunnel.
This application simplifies the system described in U.S. application Ser. No. 14/733,962 and PCT application US2015/034765, by eliminating the parachute. The parachute disclosed in those applications ensured a soft landing for the UAV, providing safety for any persons on the ground, protection for property on the ground, and preservation of the UAV.
A UAV with less than 2 kg all up weight is subject to fewer government regulations, because it is so much safer than heavier UAVs. The kinetic energy in a collision is low enough to reduce serious injury to persons and objects. To meet the 2 kg weight restriction while including a parachute sized large enough to ensure a soft landing is challenging. While developing and testing a power line inspection UAV we found we were almost always alone in the right of way near the transmission line. People are never allowed to live under transmission lines and while they occasionally pass under them to farm, park, or hike; the majority of lines are located away from urban areas. Similarly, very few structures are built under transmission lines. The right of way is a corridor free of obstructions to flight above the towers and lines and with few people, vehicles, or structures below the lines.
The likelihood of a flyaway is low and the likelihood of a person not involved with the flight being present in the right of way is low, so the likelihood of both events occurring at the same time and place is very, very low. While it may seem counterintuitive when considering only the flyaway scenario, it may be safer considering all UAV scenarios to have a lighter UAV with a simple shutdown in case of flyaway. Looking at only the flyaway problem, a parachute definitely adds safety for persons on the ground, protection for property on the ground, and cushioning for the UAV itself. However the parachute adds dead weight, so requires larger motors, propellers, and other powertrain components. Adding all the larger components and parachute increases the airframe weight, thus kinetic energy during flight, and thus risk during any type of collision. Many other things may go wrong even with flights entirely within the right of way. Thus if one multiplies the probability of occurrence times the severity of the result and adds them up for all the possible failures, it may be safer overall to have a lighter airframe without a parachute, as disclosed here. Typically the fewer components overall, the more reliable a system is.